JP4633344B2 - Tires for passenger cars with excellent groove wandering characteristics - Google Patents

Description

  The present invention relates to a tire for a passenger car having excellent groove wandering properties.

  Conventionally, a rain groove formed on the road surface of an American highway or the like is one of the factors that have a large influence on the straightness of a vehicle. A rain groove is a groove extending in the tire running direction formed at regular intervals in the road surface width direction, and is generated when a part of a land portion facing the groove extending in the circumferential direction of the tire tread falls into the rain groove. The force causes a wandering phenomenon, which affects straightness. This phenomenon is known to be remarkable particularly in a vehicle having a circumferential groove extending straight in the tire circumferential direction.

  Therefore, when developing a tread pattern for a pneumatic tire for passenger cars, in order to suppress this phenomenon of groove wandering, it is a major issue to arrange the straight main groove of the tire at an appropriate position. There are proposals for this purpose (Patent Documents 1 and 2 below).

  However, especially in tire patterns with 4 or more circumferential grooves provided along the tire width direction, the behavior of each circumferential groove with respect to the rain groove (how to sink) is different. It is not easy to obtain a proper arrangement position.

  On the other hand, the arrangement position of the circumferential groove and the circumferential groove width are limited by other characteristics and design restrictions, and the degree of freedom is small.

  As described above, in the tread pattern in which four or more circumferential grooves are arranged in the tire width direction due to design restrictions and other tire requirement characteristics, the arrangement of the circumferential grooves having good groove wandering characteristics is determined. It is difficult, and a lot of man-hours are necessary for examination.

For this reason, tires shipped to North America with rain-groove road surfaces are mainly ones with 1 to 3 circumferential grooves due to concerns about groove wandering characteristics, but emphasis is placed on comfort such as noise and ride comfort. In such a case, it is necessary to make the tread rubber block relatively small, and tires having four or more circumferential grooves are also required to have excellent groove wandering properties.
Japanese Patent Laid-Open No. 8-53004 JP 2002-120516 A

  The present invention has been made in view of the above points, and provides a tread pattern passenger car tire having four or more circumferential grooves provided in the tire width direction, which has excellent groove wandering properties. The purpose is to do.

  The present inventor can evaluate the groove wandering property of a tire in a short time by using an image analysis process by transferring an image of a tire tread pattern and an image of a rain groove on a road surface. It has been found that a tire excellent in groove wandering property can be obtained by setting the figure of merit within a predetermined range, and the present invention has been completed.

That is, the present invention is a method for designing a tire for a passenger car having a tread pattern having four or more circumferential grooves provided side by side in the tire width direction,
For a tire, while creating a tire groove information image in which a tread pattern is divided into constant pixels with a size of p (mm),
For a road surface in which rain grooves are formed at regular intervals in the road surface width direction, create a road surface information image in which the size is divided into constant pixels of p (mm),
For the tire groove information image, 0 is assigned to the pixel corresponding to the groove portion, and 1 is assigned to the pixel corresponding to the land portion. For the road surface information image, 0 is assigned to the pixel corresponding to the non-groove portion, and the pixel corresponding to the groove portion. 1 is assigned to each of the road surface information image 1 and the road surface information image 2 is assigned 0 to the pixel corresponding to the non-groove portion and -1 is assigned to the pixel corresponding to the groove portion. , Assign a value other than 0 and 1 to the rightmost pixel of each non-groove, and for the road surface image information 2, assign a value other than 0 and -1 to the leftmost pixel of each non-groove,
The tire groove information image and the road surface information image are transferred at a certain relative position to calculate a wandering value as an index of lateral force at the relative position,
In the case of the transfer process, when the tire groove information image and the road surface information image 1 are multiplied by the numerical values of corresponding pixels, and 1 is calculated continuously from the portion where the values other than 0 and 1 are calculated Are replaced with 0 to extract a numerical value that produces a leftward force, and are multiplied by the numerical values of corresponding pixels in the tire groove information image and the road surface information image 2 to obtain values other than 0 and −1. In the case where −1 is calculated continuously from the calculated part, a value that generates a rightward force is extracted by replacing these with 0, and the total value of the extracted values is calculated to obtain the wandering value. Get,
While sliding the relative position between the tire groove information image and the road surface information image pixel by pixel in the tire width direction, the wandering value at each relative position is calculated until the sliding amount reaches one interval amount of the rain groove, The difference between the maximum value and the minimum value of the wandering value in one interval amount is calculated to obtain the wandering performance index W of the tread pattern,
The tread pattern is calculated by calculating the wandering performance index W for each pattern while changing the circumferential groove arrangement and groove width, and the tread pattern is determined as a tread pattern. There is a design method for tires.

(Where, W is the tread pattern wandering performance index, p is the pixel size (mm) used in image processing when calculating the wandering performance index, L is the tire contact length (mm), and a is The coefficient is 0.6 to 0.7.)

With the present invention, it is possible to provide a tire for a passenger car that is excellent in groove wandering property, and therefore can improve the straight traveling performance of the vehicle on the road surface on which the rain groove is formed.

  Hereinafter, matters related to the implementation of the present invention will be described in detail.

1. Tread pattern wandering performance index (1) Analysis of lateral force generation mechanism The lateral force generation mechanism when the land portion of the tread pattern falls into the rain groove was clarified by FEM (finite element method) analysis.

  Specifically, the deformation amount of the rubber block was calculated from the average contact force generated in the block of the tire tread pattern using the tire contact pressure information obtained from the tire contact test and the like, and an FEM contact model was created. Then, while changing the contact relative position of the rain groove and the rubber block (see FIG. 1), the lateral force generated in the block when the rubber block fell into the groove at each relative position was obtained.

  As a result, as shown in FIG. 2, the lateral force generation state when the land portion of the tread pattern fell into the groove was found to be linear with respect to the relative positional relationship between the rubber block and the groove. That is, in FIG. 2, the lateral force was obtained for each of the three levels of 1, 3 and 5 as the longitudinal load applied to the rubber block. In either case, the lateral force increases as the relative position between the rubber block and the groove increases. Was found to grow proportionally.

  From this, the numerical values assigned to each pixel of the tire groove information image and road surface information image described later can be converted into bits (binary encoding). Therefore, the wandering performance index as an index of the groove wandering property is as follows. It can be calculated by the procedures (2) to (4).

(2) Creation of image First, a tire groove information image for each tire and a road surface information image for each road surface are created. At this time, both images are divided into pixels of the same size. Here, the pixel size p, that is, the resolution of the image is preferably 0.05 to 0.2 mm, and more preferably 0.08 to 0.12 mm from the viewpoint of accuracy of calculation results and calculation man-hours. .

  The tire groove information image has the number of pixels determined according to the contact width in the tire width direction based on the number of grooves in the circumferential direction of the tread pattern, the groove position, the groove width, and the contact width, and the tire circumferential direction Is created as a 1-by-n matrix with 1 pixel.

  Specifically, for example, from the tire ground contact shape shown in FIG. 3, the form (information) about the contact width and the circumferential groove is extracted as shown in FIG. The tire ground contact shape shown in FIG. 3 has a total of seven circumferential grooves, including four main grooves (1) having a relatively large width and three narrow grooves (2) having a small width. In addition, a plurality of lateral grooves (3) and sipes (4) extending in a tire width direction are provided. In FIG. 3, L is a tire contact length, and M is a tire contact width. In the tire width direction, the entire ground contact width is divided by the predetermined pixels, and the tire circumferential direction is one pixel.

  In the present invention, the circumferential groove is not limited to a groove having a somewhat large groove width generally called a main groove, and is generally called a sipe as long as it is a straight groove (non-groove portion) extending in the tire circumferential direction. Such a narrow groove width is also included.

  On the other hand, the road surface information image is an image in which rain grooves are formed at regular intervals in the width direction of the road surface, so that the groove portion and the non-groove portion are repeatedly arranged at a predetermined interval, and the number of pixels in the width direction and the tire running direction is determined. Is determined according to the tire groove information image that is superimposed when the following transfer process is performed.

  As for the tire groove information image, as shown in FIG. 5A, “1” is assigned to the pixel corresponding to the land portion of the tread pattern, and “0” is assigned to the pixel corresponding to the groove portion. As for the road surface information image, as shown in FIG. 5B, the road surface information image 1 in which “0” is assigned to the pixel corresponding to the non-groove portion and “1” is assigned to the pixel corresponding to the groove portion, and FIG. As shown in c), a road surface information image 2 is created in which “0” is assigned to the pixel corresponding to the non-groove portion and “−1” is assigned to the pixel corresponding to the groove portion. The reason for creating two images for the road surface information image in this way is to consider the case where a leftward force and a rightward force are generated in the tire traveling direction. That is, as shown in FIG. 1, when the left end portion of the tire land portion is applied to the rain groove, a lateral force is generated in the left direction, whereas the right end portion of the tire land portion is applied to the rain groove although not shown. In this case, a lateral force in the right direction is generated, so that both cancel each other out.

(3) Image transfer processing (calculation of wandering value)
Next, the tire groove information image and the road surface information image are transferred (array operation) at a certain relative position, and a wandering value that is an index of lateral force at the relative position is calculated. The wandering value is calculated by the following formula.

Wandering value = SUM {(tire groove information image × road surface information image 1) + (tire groove information image × road surface information image 2)}
That is, the tire groove information image is superimposed on the road surface information image at a certain relative position, and the numerical values of the corresponding pixels of the tire groove information image and the road surface information image 1 are multiplied, and the tire groove information image and the road surface information are also multiplied. The wandering value is obtained by multiplying the numerical values of the corresponding pixels with the image 2 and calculating the sum of these values. In that case, only the portion where the land portion of the tire groove information image and the groove portion of the road surface information image overlap is calculated as “1” or “−1”, and “0” is obtained for the other pixels. Will be calculated.

  However, if the total value is simply calculated by multiplying in this way, it is assumed that a lateral force is generated even when the land portion of the tire as shown in FIG. 6A covers the entire groove portion of the road surface. Will be calculated. Moreover, since the direction of the lateral force generated differs depending on whether the left or right end of the land portion of the tire falls into the groove on the road surface as described above, it is necessary to extract a numerical value multiplied in consideration of this point. Therefore, in more detail, the numerical values of the corresponding pixels in the tire groove information image and the road surface information image 1 are multiplied to extract a numerical value that generates a leftward force according to a predetermined condition, and the tire groove information image and the road surface information are extracted. The wandering value is obtained by multiplying the numerical values of the corresponding pixels with the image 2, extracting the numerical value that generates the rightward force according to a predetermined condition, and calculating the sum of these values.

  That is, with respect to the road surface image information 1 for determining the leftward force, as shown in FIG. 5B, “150” is assigned to the rightmost pixel of each non-groove portion, and the road surface image information 2 for determining the rightward force. As shown in FIG. 5C, “150” is assigned to the pixel at the left end of each non-groove portion, and transfer with the tire groove information image is performed.

  Then, as shown in FIG. 6A, when the land portion of the tire covers the entire groove portion of the road surface, multiply the tire land portion “1” by “150” at the right end of the road surface non-groove portion. By combining them, a large value “150” is calculated. On the other hand, as shown in FIG. 6B, when the land portion of the tire falls so that a force is generated in the left direction with respect to the groove portion of the road surface, each pixel is formed only by the overlapping portion of the tire land portion and the road surface groove portion. “1” is calculated for, and a large value “150” is not calculated. Therefore, when “1” is continuously calculated from the portion where such a large value is calculated, it is determined that the leftward force is not generated (the tire land portion does not fall into the groove portion of the road surface). Then, by replacing this with “0”, only the leftward force is extracted. FIG. 7A shows an example of the transfer result before extraction, and the transfer result shown in FIG. 7B is obtained by performing the extraction process as described above.

  Also, in the relative position shown in FIG. 6B, in the transfer process between the road surface information image 2 and the tire groove information image, as shown in FIG. 6C, the tire land portion “1” and the road surface non-groove portion Since a large value of “150” is calculated by multiplying by “150” at the left end, it is determined that no rightward force is generated in this portion, and this is replaced with “0”. In this way, the correct wandering value considering the leftward force and the rightward force is calculated.

(4) Calculation of Wandering Performance Index Next, while sliding the relative position between the tire groove information image and the road surface information image one pixel at a time in the tire width direction, each slide amount reaches one rain groove interval amount. The wandering value at the relative position is calculated according to the above (3). Then, the wandering performance index W of the tread pattern is obtained by calculating the difference between the maximum value and the minimum value of the calculated wandering value.

  Here, the distance between the rain grooves is one pitch of the rain grooves, that is, the distance from the end of a certain groove to the end of the adjacent groove. The rain groove road surface of the US expressway is the width of the groove. Is 2.4 mm, and the width of the non-groove portion is 16.6 mm, the distance between the gaps is 19.0 mm.

  FIG. 8 is a graph showing the change of the wandering value with respect to the slide amount of a certain tread pattern, and the difference between the maximum value and the minimum value of the wandering value is calculated as the wandering performance index.

2. Derivation of the above formula (1) When the wandering performance index W is calculated by the method 1 for a number of commercially available tires having four or more circumferential grooves, a tread pattern having a value of W or less is found. In addition, when an actual vehicle was evaluated, all were inferior in wandering performance. Table 1 shows a part of the evaluation results. Here, the pixel size is p = 0.1 mm, the road surface is a rain groove of a US highway, and the groove width is 2.4 mm and the non-groove width is 16.6 mm.

Next, no. About each tire 10-17, according to the following 3 methods, the arrangement | positioning of the circumferential direction groove | channel and the appropriate value of a groove width were determined, and the improved tire was each produced based on it. And about each tire, while performing the experimental measurement of wandering property by a bench test, actual vehicle evaluation was implemented. Table 2 below shows land widths and groove widths m1 to m8 (see FIG. 4) of the tread pattern after improvement of each tire. In addition, the arrangement | positioning and groove width of the circumferential direction groove | channel of this tread pattern are left-right symmetric centering on the center fine groove 2 with the groove width of m8.

As a result, no. As shown in Table 3, the wandering performance indexes of the improved tires 10 to 17 are all 50 or less, and the experimental measured values of the lateral force are all small, and the groove wandering performance in the actual vehicle is also good. It turned out to be excellent.

No. 12 and No. For the 17 tires, the arrangement in the circumferential direction during the improvement study (the pattern in which the wandering performance index is minimized when the number of repetitions of pattern change and wandering performance index calculation in the method 3 below is about half) Tires were produced based on the appropriate values for the groove widths, and wandering test measurements and actual vehicle evaluations were performed in the same manner. Table 4 shows the widths m1 to m8 of the land portion and the groove portion of the tread pattern, and shows the wandering performance index and each experimental result.

  As a result, no. The wandering performance index for both 12 and 17 was 51. As for No. 12, since the contact length was long, the experimental measurement value of the lateral force was large, and therefore the groove wandering property in an actual vehicle was inferior. In contrast, no. As for No. 17, since the contact length was short, the experimental measurement value of the lateral force was small, and therefore the groove wandering property in the actual vehicle was excellent.

  In the bench test, the lateral force generated by running the tire at a speed of 20 km / h and a slip angle of 0 ° on a running road surface with a drum (moving one groove per rotation) with a rain groove on the surface is used. It was measured. The difference between the maximum value and the minimum value of the lateral force when the drum was rotated once was obtained, and a value obtained by dividing the average value of the values at 128 rotations of the drum by the load was taken as “experimental measurement value”.

  In addition, the actual vehicle evaluation performance was determined by performing a test drive on an actual rain groove surface in the United States and performing sensory evaluation.

FIG. The relationship between the contact length and the wandering performance index is shown for each of the tires 1-17. From this figure, it was found that when the contact length is 150 mm and the wandering performance index W is 50, the groove wandering property is in the pass region. In addition, the boundary line between the pass area and the fail area has an inclination, and the coefficient a is 0.67 in this survey. From the above, the following formula (1) is obtained.

  Here, L is a contact length under the condition where a predetermined air pressure is applied to the tire and actually mounted on the vehicle, a is a weighting factor that the contact length affects the wandering performance index, and a = 0 .6 to 0.7, preferably a = 0.67.

3. Tire production (design of tread pattern)
A tire that satisfies the above formula (1) can be produced, for example, as follows.

  First, for the basic tread pattern, a tire groove information image is created based on the number of circumferential grooves, groove position, groove width, and contact width, and a road surface information image 1 and a road surface information image 2 are created for the road surface. These creation methods are as described in 1 (2) above. Subsequently, the wandering performance index of the basic tread pattern is calculated according to the above 1 (3) and (4).

  Then, with respect to the circumferential groove position and groove width allowance set in a range that does not affect other performances in advance, the basic tread pattern is sequentially changed by random number generation, and the wandering performance index is set for each pattern. Repeat the calculation. That is, for the basic tread pattern, the number of circumferential grooves is determined according to the application of the tire, and the position and width of the circumferential groove are determined to some extent according to the application, so the required characteristics for that The wandering performance index is calculated for each pattern while changing the groove position and the groove width within a range not impairing the above. The random number generation can be performed using known random number generation software.

  Thus, by repeating the pattern change and the calculation of the wandering performance index, the appropriate values for the circumferential groove arrangement and groove width are determined. More specifically, a pattern that satisfies the above formula (1) and has the lowest wandering performance index is determined as a tread pattern by repeating a predetermined number of times (for example, 500 to 1000 times). In addition, since the calculation time of one time is very short, even if it repeats 500-1000 times as mentioned above, it can calculate with about 3 minutes with a normal personal computer.

  Thus, the groove wandering property can be improved by setting the arrangement of the circumferential grooves and the groove width within a range satisfying the above-described expression (1). In addition, conventionally, man-hours have been devoted to determining appropriate values such as circumferential groove arrangement of such patterns, but the above-described method can be implemented in a short time on a general personal computer and is reliable. Is also expensive.

It is a schematic diagram which shows the positional relationship of the rain groove of a road surface, and the rubber block equivalent to a tire land part. It is a graph which shows the relationship of the lateral force with respect to the relative position of a rain groove and a rubber block. It is a figure which shows an example of the contact shape of a tire. It is a figure which shows an example of the tread pattern which extracted only the contact width and the circumferential groove | channel. (A) is a tire groove information image, (b) is a road surface information image 1, (c) is a figure which shows the example of the road surface information image 2. FIG. It is a schematic diagram which shows the positional relationship of the rain groove of a road surface, and the land part of a tire, (a) is the state in which the land part was completely applied to the groove, (b) and (c) are the states which generate | occur | produce left direction force. (B: road surface information image 1, c: road surface information image 2). (A) is a graph which shows an example of the image transfer result before extraction, (b) is a graph which shows an example after extraction processing. It is a graph which shows the change of the wandering value with respect to the slide amount. It is a graph which shows the relationship between tire contact length and a wandering performance index.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Main groove (circumferential groove) 2 ... Narrow groove (circumferential groove) L ... Tire contact length M ... Tire contact width

Claims (1)

A method for designing a tire for a passenger car having a tread pattern having four or more circumferential grooves provided in the tire width direction,
For a tire, while creating a tire groove information image in which a tread pattern is divided into constant pixels with a size of p (mm),
For a road surface in which rain grooves are formed at regular intervals in the road surface width direction, create a road surface information image in which the size is divided into constant pixels of p (mm),
For the tire groove information image, 0 is assigned to the pixel corresponding to the groove portion, and 1 is assigned to the pixel corresponding to the land portion. For the road surface information image, 0 is assigned to the pixel corresponding to the non-groove portion, and the pixel corresponding to the groove portion. 1 is assigned to each of the road surface information image 1 and the road surface information image 2 is assigned 0 to the pixel corresponding to the non-groove portion and -1 is assigned to the pixel corresponding to the groove portion. , Assign a value other than 0 and 1 to the rightmost pixel of each non-groove, and for the road surface image information 2, assign a value other than 0 and -1 to the leftmost pixel of each non-groove,
The tire groove information image and the road surface information image are transferred at a certain relative position to calculate a wandering value as an index of lateral force at the relative position,
In the case of the transfer process, when the tire groove information image and the road surface information image 1 are multiplied by the numerical values of corresponding pixels, and 1 is calculated continuously from the portion where the values other than 0 and 1 are calculated Are replaced with 0 to extract a numerical value that produces a leftward force, and are multiplied by the numerical values of corresponding pixels in the tire groove information image and the road surface information image 2 to obtain values other than 0 and −1. In the case where −1 is calculated continuously from the calculated part, a value that generates a rightward force is extracted by replacing these with 0, and the total value of the extracted values is calculated to obtain the wandering value. Get,
While sliding the relative position between the tire groove information image and the road surface information image pixel by pixel in the tire width direction, the wandering value at each relative position is calculated until the sliding amount reaches one interval amount of the rain groove, The difference between the maximum value and the minimum value of the wandering value in one interval amount is calculated to obtain the wandering performance index W of the tread pattern,
The tread pattern is calculated by calculating the wandering performance index W for each pattern while changing the circumferential groove arrangement and groove width, and the tread pattern is determined as a tread pattern. Tire design method.

(Where, W is the tread pattern wandering performance index, p is the pixel size (mm) used in image processing when calculating the wandering performance index, L is the tire contact length (mm), and a is The coefficient is 0.6 to 0.7.)

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